Imagery data processing systems often require that a stored image be accessed and displayed at the same time that a new image is being received. Moreover, the data rate of incoming digital data from a source of imagery signals is not always the same as the data rate of a destination device. For example, captured imagery data from a 20 Hz, Mega-Pixel camera may be used to drive a 60 Hz, high resolution monitor. Similarly, writing imagery data obtained from a four-minute scan of a 2 k pixel by 3 k line scan of 35 mm film onto a high resolution video device, such as an HDTV screen, requires the frame rate to be increased to one-thirtieth of a second. A system which converts between PAL and NTSC television standards (requiring a change in frame rate from 50 to 60 Hz) is yet another example of where the differential data rate problem exists.
Conventionally these problems have been addressed by switching between a pair of image memory buffers, and blanking the destination monitor while the next (incoming) image is being recorded. Namely, an additional or redundant storage facility is employed, or the transfer of the contents of the image memory to a display device is inhibited until loading of the new image is complete. These mechanisms neither provide for the loading of a new image in memory during the same time that a continuous output is being supplied to a destination (display) device, nor do they handle differential data rates for destination and source.